net: ag71xx: add MODULE_DESCRIPTION

Now that COMPILE_TEST is enabled, it gets flagged when building with
allmodconfig W=1 builds. Text taken from the beginning of the file.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240905194938.8453-3-rosenp@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/atheros/ag71xx.c

@@ -2033,4 +2033,5 @@ static struct platform_driver ag71xx_driver = {
 };
 
 module_platform_driver(ag71xx_driver);
+MODULE_DESCRIPTION("Atheros AR71xx built-in ethernet mac driver");
 MODULE_LICENSE("GPL v2");